Christophe Chatelain

Finite-Size Scaling Study of the Surface and Bulk Critical Behavior in the Random-Bond Eight-State Potts Model

The self-dual random-bond eight-state Potts model is studied numerically through large-scale Monte Carlo simulations using the Swendsen-Wang cluster flipping algorithm. We compute bulk and surface order parameters and susceptibilities and deduce the corresponding critical exponents at the random fixed point using standard finite-size scaling techniques. The scaling laws are suitably satisfied. We find that a belonging of the model to the 2D Ising model universality class can be conclusively ruled out, and the dimensions of the relevant bulk and surface scaling fields are found to take the values

A far-from-equilibrium fluctuation–dissipation relation for an Ising–Glauber-like model

y_h=1.849

Softening of first-order transition in three-dimensions by quenched disorder.

,

Bond dilution in the 3D Ising model: a Monte Carlo study

y_t=0.977

Monte Carlo study of phase transitions in the bond-diluted 3D 4-state Potts model

,

Mesoscopic rings with spin-orbit interactions

y_{h_s}=0.54

A temperature-extended Jarzynski relation: application to the numerical calculation of surface tension

, to be compared to their Ising values: 15/8, 1, and 1/2.

Size Effect on Magnetism of Fe Thin Films in Fe/Ir Superlattices

We derive an exact expression of the response function to an infinitesimal magnetic field for an Ising–Glauber-like model with arbitrary exchange couplings. The result is expressed in terms of thermodynamic averages and does not depend on the initial conditions or on the dimension of the space. The response function is related to time-derivatives of a complicated correlation function and so the expression is a generalization of the equilibrium fluctuation–dissipation theorem in the special case of this model. Correspondence with the Ising–Glauber model is discussed. A discrete-time version of the relation is implemented in Monte Carlo simulations and then used to study the ageing regime of the ferromagnetic two-dimensional Ising–Glauber model quenched from the paramagnetic phase to the ferromagnetic one. Our approach has the originality to give direct access to the response function and the fluctuation–dissipation ratio.

Aperiodicity-Induced Second-Order Phase Transition in the 8-State Potts Model

We study by extensive Monte Carlo simulations the effect of random bond dilution on the phase transition of the three-dimensional 4-state Potts model which is known to exhibit a strong first-order transition in the pure case. The phase diagram in the dilution-temperature plane is determined from the peaks of the susceptibility for sufficiently large system sizes. In the strongly disordered regime, numerical evidence for softening to a second-order transition induced by randomness is given. Here a large-scale finite-size scaling analysis, made difficult due to strong crossover effects presumably caused by the percolation fixed point, is performed.

Probability distributions of the work in the two-dimensional Ising model

Abstract.We study by Monte Carlo simulations the influence of bond dilution on the three-dimensional Ising model. This paradigmatic model in its pure version displays a second-order phase transition with a positive specific heat critical exponent